The present invention relates generally to a process for forming decorative trim strip.
The prior art discloses several processes of forming decorative trim strip where metal strip or metal foil is passed through an extrusion die together with thermoplastic material. The thermoplastic material forms a layer on both sides of the metal strip or foil to form a composite strip. The composite strip, with the metal layer embedded between the layers of thermoplastic material, is then formed into a shaped composite strip of a desired cross section by passage through conventional shaping means such as nipping and forming rolls.
In such processes, the metal component may be coated on one or both sides with an adhesive that is compatible with the surrounding thermoplastic material prior to its passage through the extrusion die where the thermoplastic material is deposited.
The material used for the metal strip or foil is usually stainless steel or aluminum. The thermoplastic material is normally clear polyvinyl chloride (PVC), cellulose acetate butyrate (CAB), or the like.
In such conventional processes, however, there is difficulty in forming decorative trim strip having acute angles or complicated cross sectional shapes. This is caused by increasing resistance generated by the extrudate as it is passed through successive forming rolls. In order to form a decorative trim strip having a smooth surface and a uniform cross sectional shape, it is necessary, with such prior art processes, to restrict the shape of product to simple cross sectional shapes. For example, prior art processes can form uniform and smooth decorative trim strips having C-shaped or shallow V-shaped cross sections without significant difficulty. Such shapes are capable of being readily formed from the composite layered strip without the forming process generating excessive resistance that would detrimentally affect the product.
It, however, the metal layer is stainless steel or if the thickness of the thermoplastic material is excessive, even these simple shapes may be difficult to form with the desired quality. This is due to the greater resistance these materials generate when subjected to forming.
The present invention is a significant improvement over such prior art processes because it significantly reduces the resistance of the composite strip to forming operations. By reducing the resistance to forming the present invention, it allows more complex cross sectional shapes to be produced or allows the use of stronger metal layers. In addition, the thermoplastic material used to form the strip can be thicker or stronger without detrimentally affecting the final shaping processes.
Additional advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description or may be learned by practice of the invention. The advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly set out in the appended claims.